It’s pretty simple. Young people tend to be liberal, and old people tend to be conservative. Pundits predict the old conservatives will die out and the young liberals will overtake the voting landscape. Said young liberals get older (wiser?) and become more conservative. The young liberals of the previous generation become old conservatives, and their children become the young liberals. Rinse and repeat.
Reagan did better among younger voters than older voters
Yeah, the 'old conservative, young liberal' is not a real thing; rather, it is a specific consequence of a single generational shift: the Western (largely American) Baby Boomers, who were more conservative than either those who preceded them and followed them.
Re: the main question, the future isn't necessarily 'liberal', but it will not be 'conservative'. The world changes, this is inevitable, and if you define any societal change at all as 'liberal', then you will find yourself a frustrated 'conservative'. In many ways, modern society is more conservative than it was in the past, especially in the United States; there was a time when the majority of American workers were unionized.
